Osmium composition and method of making same



Patented July 2, 1940 OSMIUM COMPOSITION AND METHOD OF MAKING SAMEAndrew R. Devereux, Chicago, and Carl Pfanstiehl Highland Park, 111.

14 Claims.

This invention relates to a method of preparing a new osmiumcomposition.

Osmium is a very difficult metal with which to work. It has tremendousability to resist wear but on the other hand is extremely brittle andfriable and when alloyed in considerable proportions with other metalstends to make them likewise brittle and hard. Various methods haveheretofore been suggested for forming alloys of osmium into useful formsand particularly for reducing the brittleness thereof. In all of thesecases, however, the osmium has been melted with the alloying metal ormetals with the result that the body of the alloy is an osmium alloy ofrelatively low wear resistance and generally of considerable hardnessand brittleness.

In accordance with .the present invention the osmium is maintainedsubstantially in its original unmelted or pure form and is bondedtogether by relatively low melting point metal which is fluxed at a hightemperature, but substantially below the melting point of osmium.

The bonding metals employed for pen point use are preferably chosen fromthe platinum group, platinum. being particularly preferred. These metalswet the osmium most readily and at the same time have highcorrosion-resistance, high melting point and also are relativelywearresistant compared with many other metals.

Base metals may be added to the platinum group metal or for somepurposes may be em.- ployed by themselves. In those instances where highcorrosion-resistance is essential, as in connection, with pen points,the base metal should 35 be employed in such proportions that theprecious metal such as platinum or ruthenium will completely cloak theordinary lack of corrosionresistance of the base metal.

In preparing the composition, finely divided, essentially pure osmiummetal and finely divided base metal or alloys thereof are mixed. Forexample, 85 parts of metallic osmium are finely ground in a ball mill toa particle size of 40 microns or less. The grinding is preferablycarried on in the presence of a wetting agent and after this has beenevaporated the ground powder was mixed with platinum or a platinumyielding compound such as an alcoholic solution of platinum chloride.The alcohol is evaporated leaving a coating of platinum chloride uponthe osmium particles.

This mixture is reduced at 1800 to 1900 F. in an atmosphere of hydrogen,leaving a coating of platinum upon the osmium and reducing any osmiumoxide present. Ordinarily the reducing operation is carried on from oneto one and onehalf hours.

After the reduction is complete the powders are cooled say to 800 F. inan atmosphere of hydrogen and then cooled in an inert gas such as 5carbon dioxide in order to prevent absorption of hydrogen by theplatinum.

The resulting material is then lightly ground in a mortar or ball millin order to break up any clusters which may have formed and is then 10formed into particles of predetermined size and shape by pressing in adie.

It is important that the particles be pressed as nearly as possible intothe form which they are ultimately to have. For instance, a phono- 1Bgraph needle point may be shaped at this stage as near to the form ofthe tip of the needle as possible. Preferably, a sharp cone is produced.Similarly, with a pen point the material may be pressed into a sphere ora rectangular block, pref- 20 erably the latter.

This forms coherent granules which are then given a preliminary heattreatment at say 2600 F. in an inert gas in order to make them somewhatmore tough and less likely to break upon handling.

The granules are then heated to about 2000 F. in a vacuum. for 15minutes in order to remove the hydrogen and they are then heated at atemperature above 2600" F., preferably 2700 to 2800 F., for 2 to 4 hoursin an inert atmosphere.

They are then cooled from 1400 to 1500 F., the inert atmosphere replacedby hydrogen, and the temperature raised to approximately 2600 F. Thegranules are maintained for a prolonged period at this temperature in anatmosphere of flowing hydrogen. The time is preferably at least 6 hoursand normally from 12 to 18 hours. The flowing hydrogen acts as a gaseousflux and the treatment greatly improves the wear resistance of thegranules with respect to relatively soft abrasives.

Prior to the final heat treatment the granules are very wear resistantwith respect to hard abrasives, such as emery, and are relatively lessresistant to such abrasives as sandpaper or ordinary writing paper. Thefinal heat treatment does not afiect the wear resistance with respect toemery but markedly increases it with respect to sandpaper and ordinarywriting paper.

The final heat treatment has the peculiar effect of making the materialmarkedly magnetic, even though the presence of ordinarily magneticmetals be avoided so far as practicable. Granules of 85%osmium, 15%platinum, containing only such iron or nickel impurities, if any, as arenormally present in commercially pure osmium, which has been ball milledas here described,

were very highly magnetic following the heat treatment.

Boiling the osmium in hydrochloric acid to free it from iron before themixing or heat treatment did not alter its magnetic properties. Beforethe boiling it contained approximately .75% of iron.

The magnetic properties are of considerable value, particularly incertain operations such as welding, where the magnetic character of themetal is of great assistance in manipulation.

The platinum may be replaced in part by iron group metals such asnickel, iron or cobalt. For example, a granule containing 85% osmium,10% platinum, and 5% nickel maybe produced by this process.

The platinum may also be replaced in whole or in part by other platinumgroup metals. For example, a very satisfactory alloy was made whichincluded 85% osmium,"l'0% platinum and 5% rhodium. In this case thepreheating with hydrogen was carried on at 2600 F., the treatment in aninert atmosphere from 3000 to 3100 F., and the final treatment inflowing hydrogen at about 2600 F.

An alloy of 85% osmium, ruthenium and 5% platinum was preheated at 2600F., then heated in an inert atmosphereat 2800 to 3000 F. and then inflowing hydrogen at about 2600 F.

In all cases the amount of osmium should pre dominate. If the amount ofother metal is below 10% there is a tendency for the resulting granuleto become brittle, whereas above 20% there-is a tendency for porosity todevelop which becomes undesirable for some purposes when the amount ofosmium is below 70%.

For many purposes the final wear resistance improving step may bedispensed with. For example, with phonograph needles the character ofwear resistance encountered is specific and it is frequently notnecessary to employ the final heating operation.

For example, a granule contain'mg 85 parts osmium, 12% parts ofruthenium and 2 parts of nickel may be prepared by heating the pressedpowders at approximately 3100 F. for 1 hour. At temperatures of 3200 F.and above the osmium composition becomes hard and brittle. Attemperatures of 2700 F. and upwards heating for 3 hours produces fairresults. Even at 2600 F. some binding can be secured but the wear isrelatively poor. With this mixture very good results were obtained byheating at 2900 F. for 2 to 3 hours.

All temperatures are approximate because of the extreme difiiculty ofaccurate measurement at these ranges.

In a similar composition-in which the nickel is replaced by moreruthenium so that the resultant composition contains 85 parts of osmiumand 15 parts of ruthenium, the temperature range is slightly different.For this mixture the preferred range is 2800 F. ,to 3200 F., with bestresults being procured at 3200 F. or slightly below. At 2700 F. andbelow the metal does not consolidate well.

With higher proportions of nickel as, for example, 85 parts of osmium,10 parts of ruthenium and 5 parts of nickel, lower temperatures thanwith the first example are preferred. However, with proportions ofnickel in this range the nickel With a 1 to 2 hour heat treatment, 3400F. is

too high for satisfactory results and 3300 F. is somewhat dangerous.Temperatures below 2800 F. are not particularly good.

Strangely enough, with all of these compositions' the Brinell orRockwell hardness of the composition goes down as the heat treatmentincreases, but the wear resistance of the metal greatly increases. Theresulting composition is therefore relatively soft compared to fusedosmium alloys of the same composition, but has extraordinarily greatwear-resistance.

The resulting material consists of discrete unmelted small particlesbonded together by a flux of lower melting point metal. The osmiumparticles are apparently in substantially pure form and apparentlylittle of the osmium is dissolved in the flux in substantialamounts.

Preferably the bonding agent predominantly comprises one or more metalsof the platinum group other than osmium. This may be platinum,ruthenium, rhodium, palladium, or iridium, although the former two arepreferred for most purposes. Other metals such as molybdenum, tungsten,nickel, cobalt, iron, or the like, may be incorporated. For pen pointpurposes the amounts of these base metals should be low enough, asheretofore explained, that they will completely be cloaked by theplatinum group metal. For purposes not requiring such highcorrosion-resistance this necessity does not exist and the bonding agentmay be made of base metals to' a much higher degree or may consistentirely of base metals.

While the bonding material is referred to as relatively low meltingpoint, it is preferable that it have a melting point not too far belowthat of osmium inasmuch as it is desirable to heat the flux to a pointwhere it will readily wet the osmium and it is not desirable that it betoo thin or have a substantial vapor pressure when it reaches suchtemperatures. I

There is no objection to minor amounts of modifying agents in thefluxing material. Even for pen point uses, minor amounts of such metalsas beryllium, zirconium, tantalum, or columbium may be added if desired.The amount of osmium may be varied over a considerable range, butmaximum wear-resistance tends to develop as the proportion of osmium isincreased and the proportion of binder is correspondingly reduced to theminimum necessary for binding purposes For all high wear-resistanceWork, it is pre ferred that the amount of osmium exceed 50%,

,given for clearness of understanding only, and

no unnecessary limitations should be understood therefrom, but theappended claims should be construed as broadly as permissible in view ofthe prior art.

We claim:

1. The method of preparing a relatively soft,

the heat treating temperatureis above approxitough high wear resistantosmium composition which comprises mixing osmium in substantially purefinely divided form with a minor proportion of finely divided lowermelting point metal, pressing the finely divided material together toform a mass at least loosely coherent, and heating the mass first toproduce a hard material of low wear resistance and then continuing thetreatment to lower the hardness and increase the wearresistance byfluxing lower melting point metal without fluxing or dissolving anysubstantial proportion of the osmium.

2. The method as set forth in claim 1, in which the iiux consistspredominantly of platinum group metal of lower melting point than osmiumand mately 2600 F. and below 3400 F.

3. The method which comprises mixing osmium in substantially pure finelydivided form witha minor proportion of finely divided metal of lowermelting point than osmium, pressing the finely divided material to forma mass at least loosely coherent, and heating the mass for a prolongedperiod at a temperature in the range of 2600 F. to 3400 F. to produce atough, highly wear resistant osmium compound in which the osmium is inthe form of substantially pure, discrete, minute particles bondedtogether by a binder of the other metal.

4. The method which comprises mixing a major proportion of finelydivided osmium and a minor proportion of finely divided lower meltingpoint metaLincluding platinum group metal other than osmium,consolidating the mixed powders without melting the consolidatedmaterial, heat-treating the consolidated material without melting toproduce a tough, wear resistant composition, and then further heattreating the material in the presence of gaseous hydrogen at atemperature of the order of about 2600 F. for a prolonged period wherebythe wear resistance of the composition to relatively soft abrasives isincreased.

5. The method as set forth in claim 4, in which the composition of thematerial includes to 90% osmium and at least 10% of other platinum groupmetal.

6. A tough, wear resistant, osmium composition comprising approximatelyosmium in the form of substantially pure, discrete, minute particlesbonded together by 15% of a flux predominantly composed of platinumgroup metal other than osmium and produced by the process of claim 1.

7. A tough, wear-resistant, osmium composition, comprising from 70% toof osmium and at least 10% of other platinum group metal prepared by theprocess of claim 1.

8. A sintered, unmelted, composition consisting essentially of 85 partsof osmium, 12 parts of ruthenium and 2 parts of nickel prepared by theprocess of claim 1.

9. A tough, wear resistant, osmium composition comprising a predominantproportion of osmium in discrete, minute particles bonded together by aflux having a melting point lower than but approaching the melting pointof osmium, the composition having been prepared by the process of claim1.

10. A tough, wear resistant, osmiumcomposi-m tion comprising apredominant proportion of osmium in discrete, minute particles bondedtogether by a flux. predominantly composed of platinum group metal otherthan osmium, and produced by the process of claim 1.

11. A tough, wear resistant, osmium composition comprising a predominantproportion of osmium in discrete, minute particles bonded together by aflux predominantly composed of platinum, and produced by the process ofclaim 1.

12. A tough, wear resistant, osmium composition comprising a predominantproportion of osmium in discrete, minute particles bonded together by aflux predominantly composed of ruthenium, and produced by the process ofclaim l.

13. A tough, wear resistant, osmium composition comprising a predominantproportion of osmium in discrete, minute particles bonded together by aflux comprising 10 to 12 parts of metal of the class consisting ofplatinum and ruthenium together with approximately 2 to 5 parts of abase metal, the composition having been produced by the process of claim1.

14. A tough, wear resistant, osmium composition comprising a predominantproportion of ANDREW R. DEVEREUX. CAR-L PFANS'IIEHL.

